INTRODUCTION. XIX 



felt convinced from his observations, that the fluid was re- 

 ceived and rejected for the purpose of sensation. Among 

 the ground-feeders in fishes, the various species of Skate are 

 remarkable for the extent of the surface over which the olfac- 

 tory nerves are disposed, produced by numerous laminae 

 radiating from a centre, which in appearance may be com- 

 pared in form to the under surface of a mushroom, of which 

 the trunk of the nerve is the stem. In the absence of cirri 

 or feelers in the various Skate, very considerable branches of 

 the fifth pair, the nerve of touch, are distributed over the 

 angular snout with which these fish turn over the sand in 

 search of proper food. It will be recollected that the mouth 

 in this family of fishes is on the under surface. They are 

 probably among the lowest of the ground-feeders. 



Whether fishes possess any high degree of taste is a sub- 

 ject not easily proved. Obliged unceasingly to open and 

 close the jaws for the purpose of respiration, they cannot long- 

 retain food in the mouth when quite shut ; the substance if 

 of small size must be swallowed quickly, and without being 

 much altered by anything like mastication. From the car- 

 tilaginous hardness of the tongue in many species, more or 

 less covered with recurved teeth, which assist in conveying 

 food to the back part of the mouth, the sense of taste may 

 pervade the surface of the soft and fleshy portions of the 

 pharynx. 



The teeth in fishes are so constant as well as permanent in 

 their characters, as to be worthy particular attention. In the 

 opinion of the best Ichthyologists, they are second only to 

 the fins ; which, in their number, situation, size, and form, 

 are admitted to be of first-rate importance. Some fishes 

 have teeth attached to all the bones that assist in forming 

 the cavity of the mouth and pharynx ; to the intermaxillary, 

 maxillary, and palatine bones, the vomer, the tongue, the 

 branchial arches supporting the gills, and the pharyngeal 



b 2 



